3 Ultrafast Dynamics of Hydrogen Atoms in Hydrocarbon Molecules
53
3.3.1.2 Methyl-d 3 -Acetylene
In methyl-d 3 -acetylene, six three-body decomposition pathways are identified in the
CMI maps and three of them are categorized into Type I decomposition pathways
and the rest of them are categorized into Type II decomposition pathways as
[Type I: C β C γ bond breaking]
I a : CD 3 CCH
3+
→ D
+
+ C γ D
+
2 + C α C β H
+
(3.3)
I b : CD 3 CCH
3+
→ H
+
+ C γ D
+
2 + C α C β D
+
(3.4)
I c : CD 3 CCH
3+
→ D
+
+ C γ HD
+
+ C α C β D
+
(and/or D
+
+ C α HD
+
+ C β C γ D
+ )
(3.5)
[Type II: C α C β bond breaking]
II a : CD 3 CCH
3+
→ D
+
+ C β C γ D
+
2 + C α H
+
(3.6)
II b : CD 3 CCH
3+
→ H
+
+ C β C γ D
+
2 + C α D
+
(3.7)
II c : CD 3 CCH
3+
→ D
+
+ C β C γ HD
+
+ C α D
+
(and/or D
+
+ C α C β HD
+
+ C γ D
+ )
(3.8)
where the carbon atoms are labeled using α, β, γ as H–C α ≡ C β –C γ D 3 .
Confirmation of the Major Pathway The relative yields for the observed six
decomposition pathways are summarized in Table 3.1. The major pathways corresponding to Pathway I and Pathway II in methylacetylene are Pathway I a and
Pathway II a in methyl-d 3 -acetylene, respectively.
The deuteron distribution maps for Pathway I a and Pathway II a are shown in
Fig. 3.1(c) and 3.1(d). In Pathways I a and II a , the distributions of A 3 and A 6 are
denser than those of B 3 and B 6 , respectively, suggesting that the deuteron is mainly
ejected from CD 3 side. The deuteron distribution maps for Pathways I a and II a have
the same tendency as the proton distribution maps of Pathways I and II, respectively. It supports our conjecture that the ejected proton in methylacetylene originates mainly from methyl group in Pathways I and II.
H/D Exchange The proton/deuteron distribution maps for the Pathways I b , I c ,
II b , and II c are shown in Fig. 3.2. The distribution A 4 of Pathway I b in Fig. 3.2(a)
shows that the hydrogen atom in the C α H group migrates to the C γ site and a deuterium atom in the C γ D 3 group migrates to the C α C β part. Therefore, this A 4 distribution shows a decomposition pathway accompanying the H/D exchange.
Similarly, the distribution A 7 of Pathway II b in Fig. 3.2(b) shows that the hydrogen atom in the C α H group migrates to the C β C γ part and a deuterium atom in the
C γ D 3 group migrates to the C α site. Therefore, this A 7 distribution also shows a
decomposition pathway accompanying the H/D exchange.
53
3.3.1.2 Methyl-d 3 -Acetylene
In methyl-d 3 -acetylene, six three-body decomposition pathways are identified in the
CMI maps and three of them are categorized into Type I decomposition pathways
and the rest of them are categorized into Type II decomposition pathways as
[Type I: C β C γ bond breaking]
I a : CD 3 CCH
3+
→ D
+
+ C γ D
+
2 + C α C β H
+
(3.3)
I b : CD 3 CCH
3+
→ H
+
+ C γ D
+
2 + C α C β D
+
(3.4)
I c : CD 3 CCH
3+
→ D
+
+ C γ HD
+
+ C α C β D
+
(and/or D
+
+ C α HD
+
+ C β C γ D
+ )
(3.5)
[Type II: C α C β bond breaking]
II a : CD 3 CCH
3+
→ D
+
+ C β C γ D
+
2 + C α H
+
(3.6)
II b : CD 3 CCH
3+
→ H
+
+ C β C γ D
+
2 + C α D
+
(3.7)
II c : CD 3 CCH
3+
→ D
+
+ C β C γ HD
+
+ C α D
+
(and/or D
+
+ C α C β HD
+
+ C γ D
+ )
(3.8)
where the carbon atoms are labeled using α, β, γ as H–C α ≡ C β –C γ D 3 .
Confirmation of the Major Pathway The relative yields for the observed six
decomposition pathways are summarized in Table 3.1. The major pathways corresponding to Pathway I and Pathway II in methylacetylene are Pathway I a and
Pathway II a in methyl-d 3 -acetylene, respectively.
The deuteron distribution maps for Pathway I a and Pathway II a are shown in
Fig. 3.1(c) and 3.1(d). In Pathways I a and II a , the distributions of A 3 and A 6 are
denser than those of B 3 and B 6 , respectively, suggesting that the deuteron is mainly
ejected from CD 3 side. The deuteron distribution maps for Pathways I a and II a have
the same tendency as the proton distribution maps of Pathways I and II, respectively. It supports our conjecture that the ejected proton in methylacetylene originates mainly from methyl group in Pathways I and II.
H/D Exchange The proton/deuteron distribution maps for the Pathways I b , I c ,
II b , and II c are shown in Fig. 3.2. The distribution A 4 of Pathway I b in Fig. 3.2(a)
shows that the hydrogen atom in the C α H group migrates to the C γ site and a deuterium atom in the C γ D 3 group migrates to the C α C β part. Therefore, this A 4 distribution shows a decomposition pathway accompanying the H/D exchange.
Similarly, the distribution A 7 of Pathway II b in Fig. 3.2(b) shows that the hydrogen atom in the C α H group migrates to the C β C γ part and a deuterium atom in the
C γ D 3 group migrates to the C α site. Therefore, this A 7 distribution also shows a
decomposition pathway accompanying the H/D exchange.